It can be used to reach really awkward areas like above the windscreen, especially if you have a luton body .. this with a decent car wash brush that takes a water supply is all you need.

Unless absolutely essential, don't go on the roof.. not only is it dangerous, especially when wet and slippy, I've read several tales of people falling off and ruining their next holiday.. but even if strong enough, your weight can distort the roof panel and break the seals around the roof lights ..
If you must go on, use something to spread the weight, like a scaffold plank.. I've always found bare feet gave me the best 'feel' and less likely to slip.

I used to go on the roof of my RV , but it had a very strong roof, composite plywood with a rubber membrane.. quite different from most European motorhomes, it did not bend or buckle under my weight and being so big it was a lot easier to use a deck scrubber and hose to get the muck off.

Plenty of propitiatory caravan cleaning products on the market.. most have a favorite... I like Silky but you can use any car cleaners. Traffic film removers are very good.. Screwfix have one at about £3 for 2lt and if nothing else avaible use washing up liquid..

If you have an awning, now is the time to also give it a good clean.. my method is is simple, very effective and cheap..

Bucket of warm water , good squirt of Fairy and 1 cup of cheap thin bleach.

Open the awning and wash BOTH sides with a soft broom or car brush.. roll it back in while still wet and soapy.. Leave for half an hour.. open up and hose off.. brand new awning. !

personal I go up on the roof and only you are in a position to decide if your fit and agile enough to get up there and work also it depends upon your weight, apart from the above I use a hose and bucket & sponge, it doesn't take that long and it gives me the opportunity to check the condition of the ancillaries fitted on the roof, I am also sad enough to polish it with autoglym. I do it about four times a year then wash and polish the rest of the van. Back to how I do it is use a ladder with foam rubber on the part that touches the van at the edge where the roof meets the side wall.

I have a ladder with pillows taped to the top.
Can do it from each side without going on top.

I used to stand on the garage roof to reach, but that stopped when I went through. (It wasn't an accident, it was stupidity.)
Broken ankles and toes isn't good.
Instead of a month's trip to Italy I had a month in a wheelchair.

In anticipation of a reply.......
Graham, Shuttit!

Plan B:
Get a vehicle valeter to do it.

John

Life isn't about waiting for the storm to pass, it's about learning to dance in the rain.

I do mine once a year in the spring always go up bare feet bucket and long handled brush. Give a good wash with a wash n wax. While up there check everything is ok 15 minutes job done for another year.

Here a few of my thoughts :-Power/Pressure washers - If you use one make sure that you have a wide fan and keep it moving otherwise you might damage your van.TFR or Traffic Film Remover- There are a lot of different makes of TFR and a lot of them contain caustic which burn the dirt away. ALWAYS read the dilution instructions, because too strong a dilution will result in your graphics disappearing and or bleached white run marks down the side of your van.Ladders - I always use lengths of pipe insulation, which protects the van and prevents slipping. I use a multi ladder similar to Grahams (Maplins sell them)Fairy Liquid - No no no, it contains salt as well as lots of other nasties and definitely no bleach please Any good car shampoo will do the job, just make sure you use lots of water before shampoo and after as your van will be covered in fine grit.Walking on the roof - I always make a judgement call before venturing on to a customers roof.Most modern vans are OK to walk on the roof occasionally.

I don't like to walk on the roof so I open up the heki to its full extent and clean all around as far as I can reach, this includes the solar panel.
Then the outer edges are washed down from on top of a multi ladder much as everyone else uses.

I use an 'H' frame, with an 'A' step ladder secured at right angles with bungees. Rectangular wheeled
bucket, long handled soft bristled brush, Motorhome/Caravan cleaner, Black streak remover all ex Aldi or Lidl
and a fair dollop of elbow grease. If it's a bit windy add a wetsuit for good measure.
Also used the 'A' and 'H' for redoing the vinyl graphics.
Regards
Mobic